In ERCP, an exchange guidewire is threaded through a lumen or open channel of an endoscope and maneuvered to a designated site within a patient's passageway to serve as a guide for positioning a device which is used to perform a procedure. The procedure may occur within the common bile duct, the cystic duct, the pancreatic duct, or the left or right hepatic duct. The guidewire, the medical instrument, and the area near the papilla of vater or the pancreatic duct are illuminated by a fiber optic light source within the endoscope and may be viewed through the endoscope or on a video monitor using a remote imaging system. The remote imaging system assists the operator and his or her staff to continuously maneuver the guidewire to maintain its position in the ductal anatomy in view of any unexpected endoscope position changes, to compensate for active motility in the gastrointestinal tract, and to maintain guidewire position during catheter exchange procedures.
Typically, the endoscope is introduced orally and maneuvered through the alimentary canal into the duodenum. The guidewire is threaded through a lumen of the endoscope and manipulated by torquing, steering, pushing and pulling to cannulate the papilla and enter the common bile duct and, if necessary, any duct branching therefrom. To withstand these manipulations and facilitate advancement of the guidewire without kinking, the guidewire is typically made of a material that has a handling characteristic which permits the operator to have a sense of the guidewire position without excessive recourse to fluoroscopy, and a strength characteristic that can support the advancement of a medical instrument thereover without the guidewire retracting from a previously accessed duct.
Conventionally, guidewires have been made using stainless steel cores, superelastic alloys such as Nitinol, or combinations of the two. Nitinol is a presently preferred material because of its flexibility; however, Nitinol and other superelastic alloys are expensive and difficult to produce. Further, superelastic alloys do not bond well to other materials, and, as a result, several ERCP guidewires have been constructed entirely of Nitinol, for example, the guidewires described in U.S. Pat. No. 5,379,779 of Rowland et al. and in the product literature for Microvasive's Geenan guidewire. These guidewire constructions are not only expensive to construct, but they provide limited torque (in inch-pounds).
As for guidewire constructions which are only part superelastic, the bond between the superelastic material and the remainder of the guidewire is believed to compromise the guidewire's ability to faithfully transmit torque (that is, cause 360.degree. rotation of the guidewire distal end with equal rotation of the proximal end) across the bond to the guidewire distal end. Further, it has been difficult to produce a highly torquable guidewire of simple construction using superelastic alloys in conjunction with other materials.
One design which has been constructed using a superelastic distal segment in combination with a solid core is disclosed in U.S. Pat. No. 5,111,829 of de Toledo. However, the stainless steel solid core is difficult to join with the Nitinol distal segment, and no attempt is made to reduce the mass of the overall guidewire. Operators of such constructions have had difficulty in directing known guidewires presumably due to inertial forces of the guidewire which result from the transmission of torque to the guidewire distal end. The inertial force tends to cause the guidewire to turn farther than desired (a phenomena known as "whipping") which exacerbates the problem of negotiating tortuous passageways.